1. Field of the Invention
The present invention relates to a control apparatus for a people mover system, and especially to the control apparatus capable of safely coping with the occurrence of a trouble or abnormality in a power unit for supplying electric power to a driving unit of the people mover system and/or a controlling unit therefor.
2. Description of the Related Art
Conventionally, it was usual to control a people mover system, such as an escalator, a moving sidewalk and so on, at a constant moving speed. With the remarkable progress of a variable speed control technique of motors, however, it has recently been proposed to control the speed of a people mover system so as to follow a desired reference, which is arbitrarily set in accordance with the necessity.
By way of example, it is proposed to change a moving speed of a people mover system by controlling an output power of a power converting unit of the system in response to the request of a caretaker (Japanese Patent Publication JP-A-62/41183 (1987)), or of a user (the same JP-A-1 122892 (1989)), whereby an old or handicapped person can use the people mover system easily, and the energy saving is attainable. Further, in the Japanese Patent Publication JP-A-61/203092 (1986), it is disclosed that an escalator is usually operated by a commercial power source and when a person using a wheelchair is going to step in the escalator, it is operated by a variable speed controller at a reduced speed.
By the way, in a power converting unit composed of a converter and an inverter, it is well known that an unusual state, such as undervoltage, overvoltage and overcurrent, is often caused by a trouble or abnormality in semiconductor elements of the converter and the inverter and that in a control unit therefor. In the case of the undervoltage, an escalator results in stopping or, if its load is incommensurately large, reversing the motion. In the contrary case, i.e., because of the overvoltage or overcurrent, there occurs the danger of making an escalator move at an abnormally high speed.
In those cases, the safest way may be to stop an escalator. If, however, an escalator is stopped, when a person using a wheelchair is on it, it is a lot of trouble to carry him or her outside the escalator together with the wheelchair. Further, since one step of treadboards in an escalator is manufactured to be somewhat higher than that in a usual stairway, an old person encounters the difficulty in getting out of the escalator by his or her own feet. The prior art as mentioned above did not take those problems into consideration at all and therefore could not provide the safe and sufficient service for users.